1. Technical Field
The present invention pertains to a Push-to-Talk (PTT hereinbelow) server, a gate apparatus, a communication system, a program, and a communication method employing a cellular phone including a PTT function to implement a one-to-many communication between terminals.
2. Related Art
Recently, a Push-to-Talk over Cellular (PoC hereinbelow) service in which the PTT function is installed in cellular phones or cellulars to implement one-to-many calls is about to be broadly used. As a feature of this PoC service, distinct from the call service of line switching type, there is a service in which one-to-many calls can be carried out. However, due to the restriction on the bandwidth or the like, two or more persons cannot simultaneously speak; a half-duplex call service is being considered in which, like in a call service of a transceiver, after a first speaker finishes a talk, another speaker obtains the right to speak and then starts talking.
The PoC service is implemented by a PoC server including management of PoC groups (group management function), registration of members, recognition of information of attendance or non-attendance such as “absence” or “presence” of a member (presence function), and assignment of the right to talk or floor (floor control; PoC function). For the call control in the PoC server, there is employed the session initiation Protocol (SIP) as in the IP telephone and the like. After establishing a session with a communicating party, Voice over IP (VoIP hereinbelow) communication of sound and voice is conducted according to an IP address assigned to a terminal in the configuration.
In the configuration of the present PoC communication, the respective members stand on an equal footing with each other; in a released state of the floor (no one is speaking), a user pushes a call start button of a terminal to transmit a floor acquisition notification to the PoC server to resultantly get the floor. In a case where many and unspecified persons join in a PoC group, any one thereof can obtain the floor under the above condition to make a statement. In addition, the participants in the PoC group are able to equally attain information about the members participating therein in the system.
Patent article 1 discloses a broadcast system adopting the PPT technique. Also in the document, the respective members are treated as equal; a server determines one of the wireless telephones in a button depression state to which a message allocation right is given and then transmits audio data from the determined wireless telephone to the other wireless telephones in the configuration.
Additionally, patent document 2 discloses a multipoint conference system which does not employ the PoC technique and in which the respective terminals are not treated as equal, the system including a terminal only for reception and a terminal for transmission and reception.    Patent document 1: Published Japanese Translations No. 2002-536928 of PCT International Publication    Patent document 2: Japanese Patent Laid-Open Publication No. 2004-187108